1. Field
The present disclosure relates to ion exchange membrane filling compositions, method of preparing ion exchange membranes, ion exchange membranes, and redox flow batteries, and more particularly, to ion exchange membrane filling compositions including aromatic vinyl monomers having halogenated alkyl groups or quaternary ammonium salt groups, methods of preparing ion exchange membranes by using the same, ion exchange membranes prepared using the methods, and redox flow batteries including the ion exchange membranes.
This invention is derived from research conducted as part of the Energy Resources Technology Development Project supported by the Ministry of Knowledge Economy (Task administration number: 2009T100200045, Development of redox flow battery with high energy density).
2. Description of the Related Art
A general secondary battery converts electric energy into chemical energy and stores the chemical energy, during charging. Subsequently, during discharging, the battery converts the stored chemical energy into electric energy and outputs the electric energy.
Like the general secondary battery, a redox flow battery also converts electric energy by charging into chemical energy and stores the chemical energy. Subsequently, during discharging, the redox flow battery converts the stored chemical energy into electric energy and outputs the electric energy. However, in contrast to the general secondary battery, an electrode active material retaining energy in the redox flow battery is present in a liquid state, and therefore, a tank for storing the electrode active material is needed.
In particular, in a redox flow battery, each electrolyte (i.e., a catholyte and an anolyte) function as an electrode active material. A typical example of these electrolytes is a transition metal oxide solution. Thus, in a redox flow battery, the catholyte and the anolyte need to be stored in a tank as solutions containing a redox transition metal in which the oxidation state is changeable.
Like a fuel cell, a redox flow battery has a cell for generating electric energy which includes a cathode, an ion exchange membrane and an anode. The catholyte and anolyte are supplied to the cell via corresponding pumps. At the respective contact surfaces, transition metal ions included in the respective electrolytes are either oxidized or reduced. At this point, an electromotive force corresponding to the Gibbs free energy is generated. The electrodes do not directly participate in the reactions and only aid oxidation/reduction of transition metal ions included in the catholyte and the anolyte.
In a redox flow battery, the ion exchange membrane does not directly participate in the oxidation/reduction reactions and performs (i) a function of quickly transferring ions that constitute a charge carrier between the catholyte and the anolyte, (ii) a function of preventing direct contact between a cathode and an anode, and most importantly (iii) a function of suppressing crossover of electrolyte active ions that are dissolved in the catholyte and the anolyte and directly participate in the reactions.
A conventional ion exchange membrane for a redox flow battery is mainly used to selectively separate ions in an aqueous solution. Accordingly, ion mobility characteristics and film properties in the aqueous solution of the redox battery have been optimized. However, there is an unmet need in an ion exchange membrane for a redox flow battery which would have optimized ion mobility characteristics and film properties in a non-aqueous system.